Grazie x l'interessamento e le mie scuse per non aver risposto prima, in questi giorni nn ho avuto tempo.

Allora... ecco cosa ho fatto e cosa è successo:
1- copiato il file ati-driver-installer-8.42.3-x86.x86_64.run nella cartella di root
2- su root
3- sh ./ati-driver-installer-8.42.3-x86.x86_64.run

E' partita la procedura di installazione come da manualetto scaricato dal sito Ati, ho scelto "install driver" e "automatic"; la procedura è finita e mi ha inserito nel menu di Gnome la voce Ati Catalyst Driver. Peccato che se provo a lanciarla non succede nulla.
Il log dell' installazione (in /usr/share/ati) se ben ricordo, recita:

codice:
[Message] Kernel Module : Trying to install a precompiled kernel module.
[Message] Kernel Module : Precompiled kernel module version mismatched.
[Message] Kernel Module : Found kernel module build environment, generating kernel module now.
ATI module generator V 2.0
==========================
initializing...
cleaning...
patching 'highmem.h'...
assuming new VMA API since we do have kernel 2.6.x...
 Assuming default VMAP API
 Assuming default munmap API
doing Makefile based build for kernel 2.6.x and higher
make -C /lib/modules/2.6.23.1-42.fc8/build SUBDIRS=/lib/modules/fglrx/build_mod/2.6.x modules
make[1]: Entering directory `/usr/src/kernels/2.6.23.1-42.fc8-x86_64'
  CC [M]  /lib/modules/fglrx/build_mod/2.6.x/firegl_public.o
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘firegl_put_user_ptr’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:1620: warning: cast from pointer to integer of different size
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:1620: warning: cast from pointer to integer of different size
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:1620: warning: cast from pointer to integer of different size
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:1620: warning: cast from pointer to integer of different size
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘__ke_check_pci’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:1990: warning: ‘pci_find_slot’ is deprecated (declared at include/linux/pci.h:481)
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘__ke_pci_find_device’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:2019: warning: ‘pci_find_device’ is deprecated (declared at include/linux/pci.h:480)
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘__ke_vm_test_and_clear_dirty’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:2544: error: implicit declaration of function ‘ptep_test_and_clear_dirty’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘__ke_pci_find_slot’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:2852: warning: ‘pci_find_slot’ is deprecated (declared at include/linux/pci.h:481)
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘__ke_request_irq’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:2962: warning: ‘deprecated_irq_flag’ is deprecated (declared at include/linux/interrupt.h:64)
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:2962: warning: passing argument 2 of ‘request_irq’ from incompatible pointer type
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘__ke_unregister_ioctl32_conversion’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:2985: warning: ‘return’ with a value, in function returning void
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘__ke_pte_phys_addr_str’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:3536: error: implicit declaration of function ‘pte_read’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:3538: error: implicit declaration of function ‘pte_exec’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: At top level:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5439: error: expected specifier-qualifier-list before ‘kmem_cache_t’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘KAS_SlabCache_Initialize’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5478: error: ‘kasSlabCache_t’ has no member named ‘routine_type’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5479: error: ‘kasSlabCache_t’ has no member named ‘lock’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5480: error: ‘kasSlabCache_t’ has no member named ‘name’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5480: warning: cast from pointer to integer of different size
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5484: error: ‘kasSlabCache_t’ has no member named ‘cache’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5485: error: ‘kasSlabCache_t’ has no member named ‘name’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5485: error: too many arguments to function ‘kmem_cache_create’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘KAS_SlabCache_Destroy’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5508: error: ‘kasSlabCache_t’ has no member named ‘cache’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5518: error: ‘kasSlabCache_t’ has no member named ‘cache’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5520: error: ‘kasSlabCache_t’ has no member named ‘cache’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘KAS_SlabCache_AllocEntry’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5555: error: ‘kasSlabCache_t’ has no member named ‘routine_type’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5556: error: ‘kasSlabCache_t’ has no member named ‘lock’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5580: error: ‘kasSlabCache_t’ has no member named ‘cache’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5583: error: ‘kasSlabCache_t’ has no member named ‘lock’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5591: error: ‘kasSlabCache_t’ has no member named ‘cache’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c: In function ‘KAS_SlabCache_FreeEntry’:
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5619: error: ‘kasSlabCache_t’ has no member named ‘routine_type’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5620: error: ‘kasSlabCache_t’ has no member named ‘lock’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5632: error: ‘kasSlabCache_t’ has no member named ‘cache’
/lib/modules/fglrx/build_mod/2.6.x/firegl_public.c:5635: error: ‘kasSlabCache_t’ has no member named ‘lock’
make[2]: *** [/lib/modules/fglrx/build_mod/2.6.x/firegl_public.o] Error 1
make[1]: *** [_module_/lib/modules/fglrx/build_mod/2.6.x] Error 2
make[1]: Leaving directory `/usr/src/kernels/2.6.23.1-42.fc8-x86_64'
make: *** [kmod_build] Error 2
build failed with return value 2
[Error] Kernel Module : Failed to compile kernel module - please consult readme.
Qualsiasi suggerimento è ben gradito.

Grazie